Nano-fabrication involves the fabrication of very small structures, e.g., having features on the order of nanometers or smaller. One area in which nano-fabrication has had a sizeable impact is in the processing of integrated circuits. As the semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, nano-fabrication becomes increasingly important. Nano-fabrication provides greater process control while allowing increased reduction of the minimum feature dimension of the structures formed. Other areas of development in which nano-fabrication has been employed include biotechnology, optical technology, mechanical systems and the like.
An exemplary nano-fabrication technique is commonly referred to as imprint lithography. Exemplary imprint lithography processes are described in detail in numerous publications, such as United States patent application publication 2004/0065976 filed as U.S. patent application Ser. No. 10/264,960, entitled “Method and a Mold to Arrange Features on a Substrate to Replicate Features having Minimal Dimensional Variability”; United States patent application publication 2004/0065252 filed as U.S. patent application Ser. No. 10/264,926, entitled “Method of Forming a Layer on a Substrate to Facilitate Fabrication of Metrology Standards”; and U.S. Pat. No. 6,936,194, entitled “Functional Patterning Material for Imprint Lithography Processes,” all of which are assigned to the assignee of the present invention.
The imprint lithography technique disclosed in each of the aforementioned United States patent application publications and United States patent includes formation of a relief pattern in a polymerizable layer and transferring a pattern corresponding to the relief pattern into an underlying substrate. The substrate may be positioned upon a stage to obtain a desired position to facilitate patterning thereof. To that end, a patterning device is employed spaced-apart from the substrate with a formable liquid present between the patterning device and the substrate. The liquid is solidified to form a patterned layer that has a pattern recorded therein that is conforming to a shape of the surface of the patterning device in contact with the liquid. The patterning device is then separated from the patterned layer such that the patterning device and the substrate are spaced-apart. The substrate and the patterned layer are then subjected to processes to transfer, into the substrate, a relief image that corresponds to the pattern in the patterned layer.
It may be desirable to properly align the patterning device with the substrate so that a proper orientation between the substrate and the patterning device may be obtained. To that end, both the patterning device and the substrate may include alignment marks. Previous methods of facilitating alignment between the patterning device and the substrate including positioning a moat around the alignment marks to create an air (or gas) gap with a different index of refraction than the patterning device which causes an interface that can be sensed with optical techniques. However, moats maybe undesirable. More specifically, moated alignment marks are not transferred into the pattern on the substrate; moats may consume a large area; moats affect fluid flow and thus cannot be arbitrarily placed within a patterned area; and for flexible patterning devices, moats do not effectively hold the alignment mark region of the patterning device in superimposition with the formable liquid, causing pattern distortions.